cos（-585°）/sin495°+sin（-570°）的值是老师给了答案是根号2-2,要求我们写过程

cos（-585°）/[sin495°+sin（-570°）]=cos(135°-720°）/[sin(135°+360°)+sin（150°-720°）]=cos135°/(sin135°+sin150°)=(-根号2/2)/(根号2/2 +1/2)=(-根号2)/(根号2 +1)=(-根号2)(根号2 -1)=-2+根号2...